At the word, Sam, as he's known, stepped onto a plywood platform hooked to a scale. His legs as stout as fire hydrants, he wobbled and squirmed there for a few seconds while the device's digital readout bounced from 955 pounds to 953 to 964 to 952.

Close enough.

The point, after all, was much the same as your doctor's is when he or she insists on weighing you each time you darken the clinic door. Weight trends are good indicators of health in beasts, human or otherwise.

&bull What: The Oregon Zoo plans its Rabbit Romp, with Easter egg hunts every 20 minutes from 9 a.m. to 3 p.m. today. The hunts are for those ages 2 to 10, and kids need to bring their own baskets.

• Where: 4001 S.W. Canyon Road

• Cost: Egg hunts are free with zoo admission ($6.75-$9.75; free for those 2 and younger).

• Information: www.oregonzoo.org, 503-226-1561

Because zoo animals don't hunt or forage for food, as their wild counterparts must, they're prone to excess weight. And just like overfed, underexercised people, zoo animals or pets carrying too much weight can develop cardiovascular disease or diabetes. They can suffer from degenerative joint disease. Zoo animals too arthritic to move without extreme pain are euthanized.

"Keeping them thinner staves that off," Finnegan says. "And if they already do have arthritis, it makes it easier for them to get around."

Animals that aren't lean and healthy can fail to breed, or they can die prematurely.

"Dietary management," Finnegan says, "is one of the biggest challenges we have." He consults with Michelle Corse in the zoo's animal commissary to craft nutritious diets for about 2,200 animals from roughly 260 species.

Zoos typically didn't employ nutritionists until the late 1980s or early 1990s. Today, research on zoo animal nutrition lags far behind research on chow formulated for domestic critters. So zoos extrapolate from what's known about feeding livestock or pets to design diets that work for, say, zebras and tigers.

Many get commercially produced "complete feed": pellets or biscuits packed with species-appropriate vitamins and minerals. Animals such as gazelles and Pete, the black rhino, get hay, too, but quality varies depending on where it was grown and how it was cut.

"It's kind of like feeding a child," she says. "If they don't have something that motivates them ... you might get boycotts or behaviors you don't want."

Recently, for instance, a swamp monkey on a treat-free diet was misbehaving. When keepers added low-calorie vegetables to her daily fare, the monkey's behavior improved.

"They all have preferences," Finnegan says. "A lot of animals are just like people in that they really go for the high-calorie, high-fat, high-sugar foods."

Tigers and leopards are crazy for fatty goat's milk, which keepers store in spray bottles. "If they see the sprayer in your hand," he says, "they're your best friend."

What makes a polar bear lick his chops? Carrots.

Chimps will chomp whole, raw onions as if they were apples. And speaking from experience, Finnegan says, it's wise to avoid the chimps the day after onions are served.

"Elephants," he says, "really like tobacco. It used to be an old reward -- chewing tobacco or leaf tobacco."

Though the Oregon Zoo chooses instead to offer its elephants treats such as yams or raisins, Finnegan knows of a keeper who used to care for elephants at a Tennessee zoo. The fellow routinely smoked half a cigar, stubbed it out and handed the remainder to an accepting pachyderm.

Keepers use food rewards to train animals for all sorts of care-related behaviors, such as allowing blood draws or weigh-ins. Accurate weight information is critical when dosing an animal that needs anesthetizing, antibiotics, dewormers or other medications.

Keepers get some weights daily, some weekly, some monthly or less often. While Finnegan would prefer it if all the animals were regularly weighed, that's easier said than done.

For zebras, the zoo's lone giraffe and other hoofstock, scales are too slippery, says Chris Pfefferkorn, general curator. But all the predators weigh in, as do primates and the black rhino. Sea lions, knowing a fish reward is not far behind, hoist themselves up on scales. Bears, whose weights fluctuate dramatically as seasons change, are routinely weighed to track trends. Fish and insects aren't weighed, but birds and reptiles are. Scales sit atop tall posts in the California condor pens at the zoo's off-site Jonsson Center for Wildlife Conservation. Without being asked, the big scavengers flap up and perch right on them.

Sam the elephant, who stands just over 4 feet tall at the shoulder, and who has gained nearly 700 pounds since Rose-Tu delivered him, appears used to the weigh-in routine that started with a shove. As he grew, it evolved into a slick move in which his mother provided a sort of body block, helping keepers position Sam on the scale. Now, that word -- "Scale!" -- does the trick.

After steadily gaining two to five pounds a day, his weight recently dropped a bit. For the most part, he still nurses. The weight loss, Lee says, may indicate that Sam's beginning the transition from mother's milk to solid food.

"Steady," he commanded, as Sam wiggled atop the scale for the fleeting seconds it took to weigh him on Tuesday.